Grinding machine



April 9, 1957 J. H. BREISCH 2,787,869

GRINDING MACHINE Filed April 7, 1953 I 7 Sheets-Sheet 1 fie.

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April 9, 1957 J. H. BREISCH GRINDING MACHINE 7 Sheets-Sheet 5 Filed April '7, 1955 IN VEN TOR. Jaw/v A6 BEE/SCH April 9, 1957 J. H. BREISCH GRINDING MACHINE 7 Sheets-Sheet 6 Filed April '7, 1953 it; :E:

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April 9, 1957 Filed April 7. 1953 LJLJ J. H. BREISCH GRINDING MACHINE 7 Sheets-Sheet 7 IN VEN TOR. Jaw/1 Bee/sen GRINDING MACHINE John H. Breisch, Lakewood, Ohio Application April 7, 1953, Serial No. 347,373

Claims. (Cl. 51101) This invention relates to grinding machines and, more particularly, to a grinding machine especially adapted to follow the contour of a turbine blade when feathering the edge thereof.

The outer end or tip of a turbine blade, especially a blade used with turbine type airplane engines, is commonly tapered or feathered for the purpose of providing a clearance between the outer tip and the stationary part of the turbine to prevent rubbing due to expansion incident to the operation of the turbine. The feather or taper is preferably in the form of an arcuate taper on the back side of the blade at the outer tip.

The principal object of the present invention is the provision of a new and improved grinding machine adapted to accurately and economically feather the end of a turbine blade.

Another object of my invention is the provision of a new and improved grinding machine especially adapted for feathering turbine blades wherein the grinding wheel and the workholder are each capable of relative movement with respect to the other and which has means enabling easy adjustment of the position of the grinding wheel with respect to the workholder.

Yet another object is the provision of a new and improved grinding machine for grinding turbine blades in which the grinding wheel will follow the contours of a turbine blade during the grinding operation and wherein the contour which is followed by the grinding wheel may easily and quickly be changed.

Another object of the present invention is the provision of a grinding machine having a workholder adapted to support a turbine blade for movement along an are contained in a plane and a grinding wheel mounted in grinding relationship to the turbine blade positioned in the workholder and adapted to be moved along an are contained in a plane perpendicular to the plane of movement of the turbine blade. 7

Still another object of my invention is the provision of a grinding machine having a new and improved workholder for feeding a workpiece past the grinding wheel of the machine. i

A further object of my invention is the provision of a new and improved grinding machine which has a novel grinding wheel dressing mechanism in combination therewith to provide a simple and accurate means for dressing the grinding wheel whenever necessary.

Another object of my invention is the provision of a new and improved grinding machine for feathering the ends of turbine blades wherein the axis of the turbine blade to be ground is supported by a rockable workholder along a line parallel to and offset from the axis about which the workholder is rocked and wherein the grinding wheel is moved toward and away from the workholder during the grinding operation to cause the wheel to follow the contour of the blade as the workholder is rocked.

With these and other objects in view as may hereinafter appear the several features of the invention consist in the devices, combinations and arrangements of parts herenited Stat Patent 0 F ice inafter described and claimed which together with the advantages to be gained thereby will be readily understood by one skilled in the art from the following description taken in connection with the accompanying drawing in which,

Fig. 1 is a side elevational view of a machine embodying my invention;

Fig. 2 is a front elevational view of the machine of Fig. 1;

Fig. 3 is a detached enlarged end view of the workholder of the machine of Fig. 1 showing the details of the support for and construction of the workholder;

Fig. 4 is a detached plan view partly cut away of the workholder and the drive mechanism for rocking the workholder andelevating the grinding disk;

Fig. 5 is a front elevational view of the portion of the machine shown in Fig. 4;

Fig. 6 is a vertical sectional view taken along lines 6-6 of Fig. 5 and showing the details of the cam for operaing the switches which control the driving motor for the workholder;

Fig. 7 is a detached vertical sectional view along lines 7--7 of Fig. 5 and showing the details of the cam used to control the movement of the grinding wheel during the grinding operation;

Fig. 8 is a detached side elevational view of the grinding wheel dresser mechanism showing the details of the dresser and its mounting; I

Fig. 9 is a detached front elevational view of the grinding wheel dressing mechanism;

Fig. 10 is a vertical sectional view taken along line 10--10 of Fig. 9 in the direction of the arrows;

Fig. 11 is a vertical sectional view taken along line 11-11 of Fig. 9 in the direction of the arrows; and

Fig. 12 is a schematic diagram showing the electrical circuit forcontrolling the operation of the grinding machine. Fig. 13 is a sectional view of the outer tip of a turbine blade in grinding position.

..Although my invention may be embodied in various types of grinding machines where it is desirable to have the grinding wheel follow a particular contour, it is here shown as embodied in a grinding machine especially suitable for feathering the outer end or tip of turbine blades. The objects of the invention, in the illustrated and preferred embodiment, are accomplished by provision of a grinding wheel for movement toward and from a turbine blade supported in grinding position or relation thereto by a workholder adapted to be rocked about an axisoifset from but preferably parallel to the longitudinal axis of the turbine blade positioned in the workholder, and by providing adjustable means for moving the grinding wheel transverse to the axis of the turbine blade in timed or predetermined relation to the movement of the workholder so that the grinding wheel will follow the contour of the turbine blade as it is fed by the grinding wheel. I v

As shown, the grinding machine comprises a grinding wheel or disk 11 movably mounted above a workholder 12 supported on a frame or stand 13 and adapted to secure a workpiece or turbine blade 14 in a position to be operated on. by the wheel 11. The grinding wheel 11, which is located within a suitable guard, is fixed to the projecting end of a driven shaft 15 of a gear box 16 forming the right hand end of a motor 17. The motor 17 is secured to the underside of a carrier arm 18, pivotally fixed to the end of an upright or stanchion 19 of frame 13. The carrier arm extends rearwardly beyond the stanchion 19 so that the weight of the grinding wheel 11 and motor 17 may be counter-balanced by a spring 20 running from the extended end of carrier arm 18,to the side of stand 13. As the carrier arm 18 is moved about its pivot the motor 17 and the grinding wheel 11 supported thereby are moved toward and from the workholder 12. The movement of the grinding wheel 11 is along an are contained in a planeperpendicular to the longitudinal edge or axis of the turbine blade 14 positioned in the workholder 12.

The workholder 12 is fixed to a horizontal shaft 21 near the right hand endthereof so as to oscillate therewith. The shaft 21 is substantially parallel to. the axis of the grinding Wheel 11 and is rotatably supported by three bearings 22a, 22b, and 22c spaced longitudinally along the shaft and carried by base plate 23 adjustably mounted on frame 13. A reversible driving motor 24 is provided to oscillate shaft 21 and cause the workholder to rock inwardly under the grinding wheel 11 and .then outwardly to its original starting position.

The relationship of the grinding wheel 11 to the workpiece and workholder is controlled by an adjustable cam 25 mounted on the shaft'21 which cam operates to move the grinding wheel about the .pivot of the carrier arm 18.. A cam follower 26 is carried by the bottom of a yoke 27 (see Fig. 8) which'straddles the grinding tool motor 17 and is supported from the upper part thereof. The cam follower 26 will follow the contours of cam 25 as the shaft 21 is oscillated, causing the carrier 18 and the grinding wheel to move toward and away from the workholder 12. The relationship of the wheel to the turbine blade at any particular point during the grinding operation is easily predetermined by correct shaping of the cam, and by adjustment of the relationship of the cam to the cam follower. V

A grinding wheel dressing mechanism 28 is provided to enable the grinding wheel 11 to be quickly and easily dressed to maintain the proper contour for grinding an arcuate taper on the blade as illustratedin Fig. 13. The grinding wheel dressing mechanism 28 is supported .forwardly of the grinding motor by the yoke 27.

Workholder construction The details of the workholder construction are best shown in Figs. 3, 4 and 5. The workholder 12 comprises a body member 30 having a, transverse'shaft opening in the lower part thereof for re'ceivingshaft 21. The body member 30 is keyed on the shaft 21 near the end thereof adjacent the shaft bearing 22c by a key 31 so that it will rotate with the shaft. In order to prevent longitudinal displacement along the shaft 21 the workholder 12 is held against the shaft bearing 220 by a keeper nut 32 threaded onto the end of the shaft.

Each side of the body member 30 of the workholder 12 is provided with a T-shaped recess 33, the leg. of the T extending downwardly from the top edge of the side and the crosspiece of the T extending across the side at approximately the midpoint 'thereof. A transverse Work receiving bore 34 joins the two recesses. To hold the turbine blade 14 in position, clamping means are provided on each side of the workreceiving bore 34. A lower clamping plate 35 is'mounted on each side of the body member 30 in the crosspiece of the T-shaped recess 33. The top surface of each lower clampingplate 35 is of such contour as to be complementary to the contour of the surface of the blade to be held against the plate. Sliding in the leg of each T-shaped recess 33 is an upper clamping plate 36 having the lower end cut in a contour complementary to the contourjof the top side of the blade to be held by the workholder 12. The complementary .clampingsurfaces assure that the workpiece will not slip with respect to the workholder during grinding. To prevent lateral displacement of the upper clamping plates, gibs 37 are bolted to the body member 30 adjacent the sides of theleg of each T.-shaped recess 33. p

"The upper portion of the body memher30 is bifurcated providing a rectangular groove 38 parallel to thesides of the member which extends downwardly from the top thereof to a point which is just above the work receiving bore 34. Pivotally secured at the forward end of the groove 38 is a bell crank lever 40 having two lever arms 40a and 40b. The lever arm 40a is located within the groove 38 and the lever arm 40b extends downwardly from the forward end of arm 40a externally of the groove 38. The lever arm 40a mounts a dowel pin 41 which extends laterally of the sides of the arm through elongated openings 42 in each side of groove 38 and into receiving aperture 43 in each upper clamping plate 36. The lever arm 40a has a vertical bore 44 therein opening from the underside of the lever arm near the inner end of the arm to accommodate a spring 45 which acts against the bottom of groove 33 to bias the inner end of lever arm 40:: in an upward direction.

Pivotally fixed to the lower end of lever arm 40b is an operating lever 46 of the eccentric cam type. The operating lever 46 bears against a pressure plate 43 mounted in the body member 30 immediately behind operating lever 46. The operating lever 46 is cam shaped as indicated at 46a so that as the handle is moved downwardly the pivot point of the arm 40b and the operating lever 46 will move outwardly and upwardly causing the lever arm 40a to move downwardly in groove 38. The downward movement of the arm 4011 will be transmitted to the upper clamping plates 36 by dowel pin 41 causing them to move against the upper surface of the lower clamping plates 35 or against a workpiece between the clamping plates.

The turbine blade 17 is placed in the work receiving bore 34 from the right hand side of the workholder. The part to be ground is extended beyond the left side of the workholder 12 and the blade clamped into position by motion of the operating handle in a downward direction. When the workholder is rocked by shaft 21 the axis of rocking will be parallel to but offset from the longitudinal edge. or axis of the turbine blade and the turbine blade will move along an are contained in a plane perpendicular to the shaft 21.

Drive mechanism .Mounted at the end of the shaft 21 remote from the workholder 12 is the workholder drive motor 24 which oscillates the shaft 21 and rocks the workholder with respect to the grinding wheel 11. The control switches for operating the motor 24 are microswitches mounted on a switch carrier bracket 50 near the motor 24 and include an inward control switch 51, normally open, an outward control switch 52 of the reset type and normally open, and a safety switch 53, normally closed. These switches are operated. in proper sequence by a switch operating cam 54. The switch operating cam 54 is a disk comprising an arc of approximately in the illustrated embodiment and is moved into engagement with the operating mechanism of the switches when the drive motor 24 oscillates the shaft 21. The switch operating cam 54 is mounted on a stub shaft 55. Cam 54 is driven by a pinion 56 which is suitably secured to shaft 55 and which meshes with a driving gear 56a mounted on the shaft 21 adjacent bearing block 22a.

The inward control switch .51 is mounted on the switch carrier bracket 50 so that it is on the left side of the cam plate when the machine is viewed as in Fig. 5. Intermediate the forward'control switch 51 and the switch operating 'ca'm 54.isa.switch tripping lever 57 adapted to operatecontrolswitchSl. The switch tripping lever 57 has one end pivotally secured to the switch carrier plate and extends upwardly in a vertical direction past the switch S1. The free end of the trip lever is notched, and pivotally mounted in the notch 58 thereof is a latching lever 59. The latching lever.is mounted so that it extends at'right angles from the switch lever toward the switch operating cam 54 and when in this position the underside of the latchinglever rests against the bottom of thenotch 58. The free .end of the latching lever is spring biased into engagement with the bottom of the notch 58 by a latching lever tension spring 60 having its ends secured respectively to the free end of the latching lever and to the trip lever 57 at a point close to its fixed end. The free end of the tripping lever is spring biased away from the forward control switch toward the switch operating cam by a tripping lever biasing spring 61. The spring 61 is secured at one end to the free end of the tripping lever 57 and to a point on the switch carrier plate 50 at the other end. The free end of the latching arm 59 has a roller 62 rotatably secured thereto and adapted to bear against forward cam member 63 carried by the side of the switch operating cam 54. It will be seen that as the switch operating cam moves downwardly against the roller 62 the latching arm will be forced into engagement with the bottom of the notch 58 preventing the latching arm from rotating about its pivot. The tripping lever 57 will then be forced to move against spring 61 in a direction toward inward control switch 51. The movement in this direction is adapted to operate the inward control switch. When the cam 54 moves in the other direction, that is, upwardly with respect to the roller 62, the latching arm is free to move in an upward direction against the tension of spring 60. When a slight movement of the center of the roller from a line at right angles to the center line of the tripping lever 57 occurs, the force of the lever arm tensioning spring 61 will aid the latching lever in its upward movement and the tripping lever 57 will be moved toward the switch operating cam and away from the inward control switch 51 as the latching mechanism collapses. Thus it will be seen that the switch tripping lever will close the inward control switch 51 when the cam 54 moves downwardly with respect to the switch 51 and will release the switch when the switch operating cam is moved upwardly with respect to the switch 51.

Mounted on the opposite side of the switch operating cam 54 is an outward control switch 52. Outward control switch 52 is of the reset type and will remain in the open or closed position until moved to the other position. A switch button 65 extends toward the switch operating cam 54 and is adapted to be operated by cam member 66 mounted thereon. Also carried by the switch operating cam 54 is a reset cam member 67 which operates a reset lever 68, which lever is pivotally secured to the switch bracket 50 adjacent a reset button 69 on the outward control switch 52. The reset cam member cooperates with one end of the reset lever 68 and the other end bears against and operates reset button 69. As the reset cam 6'7 engages the reset lever 68 the reset button 69 is forced inwardly to move the switch to open position.

The safety switch 53 is mounted on the switch carrier plate 50 radially opposite the switch operating cam 54. The safety switch 53 is operated by a safety cam member 79 which extends radially outward from the remote end of the switch operating cam 54. Thus, if the workholder is rotated too far in the direction away from the front of the machine, as viewed in Fig. 2, the safety cam member 7% will operate to open the safety switch 53 and stop the workholder drive motor 24.

The grinding tool control cam 25 is carried by a cam block 75 which has an arcuate recess 76 therein adapted to accommodate a shoulder on the lower portion of the I cam block 75 are tapered so that the bottom er" the cam block is narrower than the top. Bolted to the tapered sides of the cam block are support extensions 81 which extend upwardly past the ends of arcuate recess 76 at a spaced distance from the ends of the grinding tool control cam 25. Setscrews 82 carried by the upper portion of the support extensions 81 protrude inwardly of the extensions and engage the ends of the grinding tool cam., These screws allow the grinding tool cam 25 to be easily adjusted in the arcuate recess 76. As the shaft 21 is oscillated the grinding tool cam 25 will act through grinding tool cam follower 26 supported by the bottom of yoke 27 to move the grinding wheel 11 supported by carrier arm 18 about its pivot, thereby moving the grinding Wheel 11 along an arc contained in a plane perpendicular to the plane of movement of the turbine blade positioned in the Workholder. This will cause the grinding wheel 11 to be moved toward and away from the workholder 12 in timed relationship to the movement of the workholder. The contour which the grinding wheel 11 follows is easily changed by adjusting the cam 25 on cam block so as to change its relationship to the cam follower 26.

Grinding wheel dressing mechanism In order to support the grinding wheel dressing mechanism 28, an internally threaded bushing 85 is secured to yoke 27 in any suitable manner in front of the grinding motor 17. A vertical lead screw 86 engages the internal threads of the bushing 85 and has fixed thereto at its lower end a dressing mechanism support 87. The dressing mechanism support 87 extends substantially horizontally from the vertical lead screw 86 and has on the underside thereof ways 88 which slidably carry an L- shaped mounting 89. One leg of the L-shaped mounting is supported on the ways 88 and the other leg extends downwardly in front of the support 87. The ways 88 are horizontal and substantially parallel to the plane of the grinding wheel so that L-shaped member 89 is capable of movement in a horizontal plane along a line perpendicular to the axis of the grinding tool wheel 11-. Also carried by the support 87 is a hand wheel 90 and horizontallead screw 91. The threads of the horizontal lead screw 91 engage a nut 92 which is supported from the underside of the leg of the L-shaped mounting which is carried on the ways 88. A miter gear 93 is mounted on the shaft of the horizotal lead screw 91 and meshes with a second miter gear 94 carried by the vertical lead screw 86 so that as the hand wheel 90 is rotated the miter gears will cause the vertical lead screw to rotate in the bushing 85 to move the dressing mechanism vertically. When the dressing mechanism is moved vertically it will also be moved horizontally in a direction perpendicular to the axis of the rotating wheel since the rotation of the hand wheel will cause the shaft nut 92 to move along the horizontal lead screw 91 and carry the L-shaped member 89 along with it.

A detent wheel 95 is mounted on the forward end of the shaft of the horizontal lead screw 91 immediately behind the hand wheel 9!). The rear face of the detent wheel has shallow recesses therein adapted to accommodate detent 97 mounted in the face of support 87. The detent 97 comprises a steel ball which is biased into engagement with the detent wheel by a detent spring 98 mounted in a cylindrical opening in the face of support 87. The detent mechanism will allow the hand wheel to be moved in either direction but will help the wheel from being accidentally moved from its proper position.

As is best shown in Fig. 10, a support block llll) is carried by-the leg of the L-shaped mounting which extends downwardly from the forward end of the support 87. The support block 100 has spaced longitudinal side walls 99 which extend perpendicularly from the block and support gibs 191 extending inwardly therefrom to form with the side walls a slideway for a slide block 102 movably mounted within the side Walls. The slide block 102 has two spaced longitudinal rails 103, extending substantially the length of its forward side. Mounted within the spaced rails 103 and capable of relative movement with respect thereto, is a rectangular spring holderpnd dressing tool support member 104. The springholder 104 has an axial bore 105 therein opening into the left end of the spring holder as the holder is viewed in Fig. 9. A compression spring 106 and its guide shaft 107 is adapted to be mounted within the axial bore 105. The spring guide shaft 107 passes through the spring 106 and threads into the inner end of axial bore 105. The spring guide shaft 107 extends outwardly beyond the support block 100 through a spring retainer clip 108, which is bolted across the ends of the rails 103. The spring guide shaft 107 has threaded thereon stop nuts 121 which are adapted to abut a tool dresser stop plate 122 carried by the end of support block 100. The spring holder 104 can'move toward grinding wheel 11 until the stop nuts 121 abut the stop plate 122.

The end of the rectangular spring holder and dressing tool support member104 opposite the compression spring 106 has a horizontal support stern 109 extending therefrom and carries at its outer end a cylindrical housing 119 having its axis substantially vertical. A dressing tool 111 is secured to a head 112 rotatably supported by housing 110. The tool dresser head is located above the upper end of the housing 110 and has a tool dresser shaft 113 extending downwardly from the tool dresser head 112 through the housing terminating in a collar which abuts the lower end of the housing 110. The tool dresser shaft 113 mounts a pinion 114 intermediate the head 112 and the upper end of housing 116 which is adapted to mesh with a rack 115. Movement of the rack 115 will cause a rotation of the shaft 113 and the dresser head 112. The rack 115 is supported by a rack stop plate 116 which is secured to the two longitudinal rails 103 in any suitable manner such as by being bolted thereto. The rack stop plate 116 has a slot 117 therein which is adapted to receive a dowel 110 extending from the rectangular spring holder. The dowel 118 operating in slot 117 will allow limited movement of the rack stop plate with respect to the rectangular spring holder 104 and head 112. A handle 119 is secured to the lower end of a bar 120 fixed to the rack stop plate 116. The handle 119 extends horizontally under the tool dresser mechanism and is pivotally supported at its inner end from the underside of the L-shaped mounting 89. Moving the handle 119 toward the grinding wheel 11 will slide the rack stop plate 116 and the slide block 102 in the slideways formed by the side walls of the support block 100.

The spring guide shaft 107 has threaded thereon stop nuts 121 which are adapted to abut a tool dresser stop plate 122 carried by the end of the support block 100. The rectangular spring holder and consequently the tool dresser will move with the slide block 102 through the action of the spring 105 and retainer 108 until the stop nuts 121 abut the tool dresser stop plate 122. When this occurs the spring holder 104 will be held against any further sideways movement by the dresser stop plates 122 but the rack 115 can be moved an additional distance toward the grinding wheel 11 by compression of the Spring 196. The spring retainer will cause the compression of the spring as the slide block 102 and rack 115 are moved sideways with respect to the spring holder 104. As the rack 115 continues to move with respect to the spring holder 104 and head 112 the head 112 will be rotated by the rack as itpasses over pinion 114.

As is best shown in Fig.'ll, the upper end 123 of the head 112 is forward or outward of the axis about which the head is rotated. The dressing tool 111 is supported radially of the axis of rotation of the head 112 by the upper end 123 and extends inwardly toward the axis of rotation which passesthrough the grinding wheel 11 when the point of the tool is against the edge of the wheel. As the head .112 is rotated the inner end dressing tool will move through an are about the axis or rotation of the head and dress arconve'x surface on the, grinding edge of the wheel complementary to the desired concavesurface on the blade. It is preferable that the feathered tip of the turbine blade have a geenrally parabolic crosssection. By support of the point for rocking movement in a horizontal plane which is below the horizontal diametrical plane of the wheel, and, therefore, at an angle to the radial plane of the wheel passing through the dressing tool point, the desired generally parabolic shape will be produced on the edge of the wheel. The edge of the wheel will be dressed to the same shape regardless of the diameter of the Wheel since the lead screws will function to move the dressing tool point along a diameter of the wheel when adjusting for ditierent wheel diameters.

From the description of the grinding wheel dressing mechanism it can be seen that the grinding wheel 11 may easily be dressed by motion of the handle 119 of the tool dresser mechanism toward the grinding wheel. This will cause the slide block 102 and the rectangular spring holder 1114, to move together a predetermined distance toward the grinding wheel carrying the dressing tool 111 into position to dress the wheel. When the dressing tool 111 is in correct dressing position, continued movement of the handle 1.19 toward the grinding wheel 11 will move the slide block 102 and the stop plate 116 relative to the spring holder and dressing tool support stem 109 causing the rack to move across the gear 114 rotating the head 112 to dress the wheel 11. When the stop dowel 118 carried by the support stem strikes the back side of the elongated opening 117 further relative movemerit between the slide block 102 and the rectangular spring holder is prevented. The movement of handle 119 is then reversed and the rack 115 and slide block 102 will move back rotating the head 112 until the front edge of the slot 117 engages the stop dowel 118 on the support stem thus completing the rocking of the dressing tool and the dressing operation. Continued movement of the handle 119 away from the grinding wheel 11 will move the dressing tool away from the grinding wheel 11 and back to its original position.

It. should be noted that the grinding wheel 11 will become smaller with use, and the point of engagement of the dressing tool will, in the illustrated embodiment, be moved inwardly and upwardly. Movement of the wheel 90 will cause the dresser tool mechanism to simultaneously move inwardly and upwardly assuring that the dressing tool 111 will always engage the grinding wheel at the correct point on its circumference.

Electrical control A reversing switch 125, shown schematically in Fig. 12, is provided to control the operation of motor 24. The reversing switch 125 is of a standard commercial type and comprises two control coils 126 and 127. When the control coil 126 is energized the electrical connections to the driving motor 24 are such that it rotates the workholder 12 inwardly so as to move the workpiece past the grinding wheel 14. Energization of the control coil 127 causes the motor to rotate in the opposite direction and move the workhoider outwardly toward its original position.

The energization of control coils 126 and 127 is controlled by control switch 5'1, normally open, switch 52, normally open, and safety switch 53, normally closed. The power for the coils 126 and 127 is supplied by power lines 128 and 129. One side of coil 126 is connected to the power line 128 through the inward control switch 51 and a starting switch 130 in parallel with the control switch 51. The other side of coil 126 is connected to power line 129 through normally closed safety switch 53.

The starting switch 131) has four terminals 131, 131', 132 and 132. When the switch is in its normal position terminals 131 and 131 are bridged by the conductor bar 133. When the switch button is pushed inwardly the bar 133' will bridge contacts 132 and 132'. The connection from the coil 126 of the reversingswitch 125 to 9 the starting switch 130 is made to terminal 132 and the terminal 132 is then connected to power line 128. The connection from the coil 126 to the power line 128 through the starting switch 130 is normally open but may be closed by pushing the starting button on the starting switch inwardly to bridge terminals 132 and 132.

The coil 127 of the reversing switch 125 is connected to the power line 129 through control switch 52. The other side of the coil is connected to power line 128 through the starting switch 130. Connection from the coil 127 is made to terminal 131 and terminal 131' is connected to power line 128. The connection from the coil to power line 128 through the starting switch 130 is normally complete since the conductor bar 133 normally bridges terminals 131 and 131.

When the starting button on control switch 130 is pushed inwardly it bridges contacts 132 and 132' which completes a connection directly from power line 128 through the reversing switch control coil 126 and the safety control switch 53 to the power line 129.- The button of starting switch 130 is held in until the cam 54 has an opportunity to close the inward control switch 51. The closing of the inward control switch 51 will complete a holding circuit for coil 126. After the motor as has rotated the shaft a predetermined distance the outward control switch 52 is closed and the inward control switch 51 opened. This completes the circuit through coil 127 the conductor bar of switch 130 bridging terminals 131 and 131 and opens the circuit through coil 126 thus causing the motor to reverse itself. When the workholder returns to its original position switch 52 is opened which stops the drive motor 24. Safety switch 53 will be operated if the drive motor 24 is not reversed at the proper time. This will open the circuit from coil 126 which deenergizes the coil and stops the-motor 24 from inward rotation.

Operation To grind or feather the outer end of a turbine blade, the blade is first inserted into the transverse work receiving bore 34 of the workholder 12.. The workholder operating lever 46 is pushed downwardly which causes the upper clamping plates 36 to exert a clamping pressure on the turbine blade holding it securely in place.- To start the machine the starting button is then pushed which completes a circuit, as shown in Fig. 12, through the inward control coil 126 of the reversing switch 125. As the workholder moves inwardly, that is in under the grinding wheel of the machine, the roller 62 engages the side of the control switch actuating cam 54 and closes the inward control switch 51. When the inward control switch 51 is closed the push button can then be released and the switch operating cam 54 will maintain the switch in closed position. When the workholder has been rotated through the desired arc the roller 62 moves in a direction which opens the inward control switch 51. Just prior to the opening of the inward control switch 51 the switch actuating cam 54 engages the switch button 65 of the outward control switch 52. This closes the outward control switch 52 and energizes the reversing coil 127 of the motor reversing switch. The motor reverses and the workholder 12 starts to move back toward its original position. As the switch actuating cam 54 reverses the direction of movement it ceases to engage the switch button on the outward control switch 52. The switch 52, however, is of the reset type and thereforeremains in closed position completing the circuit until the switch actuating cam engages the reset lever and opens it. The reset lever 68 will be engaged when the workholder 16 has returned to its original position.

While the workholder 16 is being rocked under the grinding wheel 12 and then back, the position of the grinding wheel 11 is being continuously varied by the action of the grinding wheel control cam 25. By applying proper contours to the grinding wheel control cam assists and by adjusting the cam with respect to the cam follower it is possible to predetermine the relationship of the grinding wheel with respect to the turbine blade at any point during the grinding cycle and as a result a. very accurate groove may be ground in the edge of the turbine blade. The final groove in the illustrated embodiment is the result of the combined movement of the workholder 12 rocking about an axis substantially perpendicular to the plane of the grinding wheel 11 and the movement of the grinding wheel in a plane which is perpendicular to the axis about which the workholder is being rocked.

The provision of the grinding tool dressing mechanism 28 which is supported from yoke 27 and movable with respect thereto enables the grinding wheel 11 to be dressed as often as is necessary to maintain the grinding wheel in proper grinding position. The accurate nature of the grinding work involved in feathering turbine blades 7 makes such a dressing mechanism necessary if the blades are to be ground on an economical and satisfactory basis. It can be seen from the above description that the grinding tool mechanism provided for by the present invention enables the tool to be dressed quickly and conveniently whenever required.

From the foregoing, it will be apparent that the objects of the invention heretofore enumerated and others have been accomplished and there has been provided a novel and improved contour grinding machine especially suitable for grinding turbine blades. While a preferred embodiment has been illustrated the invention is not limited to the particular construction shown and it is my intention to cover all adaptations and modifications which come within the practice of those skilled in the art to which the invention appertains and within the scopeof the appended claims.

Having thus described my invention, I claim:

1. A machine for grinding an arcuate workpiece comprising a frame, a workholder, means for supporting said workholder on said frame for rocking about an axis, said workholder including means offset from said axis. for supporting a workpiece in position to be ground, a carrier mounted on said frame for movement toward and from said workholder in a plane perpendicular. to the said axis, a grinding wheel carried by said carrier, power actuated means on said carrier for rotating said wheel, means for rocking said workholder during the grinding operation, adjustable means cooperating with said carrier for moving said carrier transversely of. said axis and in predetermined relationship to the movement of said workholder, and grinding wheel dressing means carried by said carrier comprising a dressing tool, a first member for rotatably supporting said tool, a second member slidingly supporting said first member for movement along a line perpendicular to the plane of said wheel, a third member supporting said second member for movement along said line and means yieldably interconnecting said first member and said second member whereby said first and second members are capable of relative movement when said tool is radially opposite said wheel, and gear means operatively connected to said dressing tool and rotated upon the occurrence of said relative movement.

2. In a grinding wheel dressing mechanism, a frame for supporting said mechanism, a slide block, support means mounted on said frame to slideably support said slide block for linear movement with respect thereto, a dressing tool support member slidably carried by said slide block so as to be movable in the same direction as said slide block, a dressing head rotatably supported by said support member, said support member being capable of moving a predetermined distance with respect to said support means, said slide block being movable a greater distance than the said predetermined distance with respect to said means, means connected to said slide block for moving said slide block, resilient means operatively connected to and between said slide block and said. support a 1 1 member for causing said slide block and said support member to move together through said predetermined distance and yielding to allow relative movement therebetween after said predetermined distance has been traverse'd, and gear means connected to said 'head in mesh with gearmeans connected tosaid slide block and operated by the relative movement of said support member and said slide block for producing rotation of said head.

3. A grinding Wheel dressing mechanism as defined-in claim 2 in combination with means to move the said support means along a resultant lineof two perpendicular motion components comprising a slideway member for connecting said support means to said frame and having a slideway for mounting :said support means for movement along one of said components, said slideway member being supported on said frame for movement along theother of said components, a first lead screw and a'cooperating-nut operatively connected to said supporting means formoving said supporting means along said slide Way, and a second lead screw perpendicular to said first lead screw and a cooperating nut therefor operatively connected to said slideway member for moving said member along said other component.

4. A machine for grinding turbine blades comprising a frame, a workholder on said frame, means for rotatably supporting said workholder, said workholder comprising two sets of spaced clamping plates having aligned clamping surfaces offset from and the axis of rotation of said workholder, each of said sets comprising a first clamping plate mounted in end-wise relationship to a second clamping plate and movable with respect thereto to allow said turbineblade to be inserted between the adjacent ends of corresponding plates, the clamping surface of each plate having a contour complementary to the contour of the surface of the turbine blade against which the plate bears, a carrier supported on said frame for movement toward and from said workholder, a grinding wheel carried by said carrier, motor means operatively connected to said wheel for rotating said wheel, means operatively connected to said workholder for oscillating said workho'lder duringthe grinding operation, and adjustable cam means operativelyconneeted to said carrier for varying the position of-said-grinding Wheel transverse to the axis of oscillation of said 'vt'orkholder and moving the carrier in timed relationship to the oscillation of said workholder.

5. A machine for grinding a turbine blade comprising a frame, a Workholder rotatably carried by said frame and adapted to clamp said blade in grinding position, said workholder comprising a body member having a set of clamping plates mounted on each of two opposite sides :thereof, a work receiving bore in said member extending between said clamping plates and offset from the axisrof rotation of said workholder, each, of said set of clamping plates comprising an upper and a lower clamping =plate mounted in an endwise relationship and adapted to clamp a workpiece between the adjacent ends thereof, the clamping end of each clamping plate having a contour complementary to the contour of the surface of thelurbine blade against which the clamping end of the piate bears when holding a turbine blade in position for grinding, a carrier movably mounted above said workholder, a grinding wheel and means for rotating said wheel mounted on said carrier, said carrier being adapted to swing about a pivot point to move said Wheel toward and from said workholder, a shaft for supporting and rocking said workholder about an axis substantially perpendicular to the plane of movement of said carrier and said grinding wheel, a reversible drive motor for rotating said shaft during the grinding operation, adjustable cam means carried by said shaft and cooperating with said carrier to vary the position of said grinding wheel in timed relationship to the movement of said holder, and electrical means for controlling the operation of said drive motor to rock said shaft.

References Cited in the file of this patent UNITED STATES PAT ENTS 324,907 Wilder Aug. 25, 1885 547,893 Roberts Oct. 15, 1895 626,427 Jones June 6, 1899 996,884 Richards July 4, 1911 1,014,306 Johnson Jan. 9, 1912 1 168,924 Pearson July 29, 1913 1,182,661 Dusha May 9, 1916 1,395,935 Walter Nov. 1, 1921 2,091,456 Rybick Aug. 31, 1937 2,092,895 Stevens Sept. 14, 1937 2,172,032 Philippe Sept. 5, 1939 2,225,489 Tessky Dec. 17, 1940 2,377,934 Greig June 12, 1945 2,640,477 :Norlander June 2, 1953 2,641,089 Fouquet June 9, 1953 2,721,423 Haussler Oct. 25, 1955 2,723,500 Narel Nov. 15, 1955 FOREIGN PATENTS 22.8.95 Great Britain Oct. 8, 1912 

